1. Field of the Invention
The present invention generally relates to a display panel, and more particularly, to a liquid crystal display (LCD) panel.
2. Description of Related Art
In recent years, along with development of optoelectronic technology and semiconductor technology, volume of video or image devices have been increasingly compacted making it possible of manufacturing lighter, flatter, thinner and smaller flat panel displays, and therefore flat panel displays has become increasingly popular and accordingly became the mainstream for development of display devices. Although conventional cathode-ray tubes (CRTs) have their advantages of low cost, excellent image quality, however, the disadvantages of larger space occupation due to their larger volume and high radiation harmful to eyes of users makes them unattractive. Nowadays, flat panel displays developed by combining the optoelectronic technology and the semiconductor technology, for example, such as liquid crystal displays (LCDs), organic electro-luminescent displays (OLEDs), or plasma display panels (PDPs), have gradually replaced the conventional CRT display and have become a mainstream of display devices.
Because, the LCDs have several advantageous features including thin-flat shape, lightweight, low operating voltage, low power-consumption, full colourization and low radiation, etc., they will become a mainstream of the 21st century's display devices. The LCDs are classified into a transmission type, a reflective type and a transflective type according to their light-emitting mechanisms, wherein the reflective LCDs include liquid crystal projectors and reflective liquid crystal on silicon ( LCOS), etc.
FIG. 1 is a cross sectional view of a conventional reflective LCD panel. Referring to FIG. 1, the conventional reflective LCD panel 100 comprises a first substrate 110, a second substrate 120 and a liquid crystal layer 130 disposed between the first substrate 110 and the second substrate 120. The first substrate 110 comprises a glass substrate 110a, an electrode layer 112, a protective layer 114, a colour filter film 116 and a first alignment film 118, wherein the electrode layer 112 comprises alumina material. The electrode layer 112 is disposed on the glass substrate 100a and the protective layer 114 is disposed on the electrode layer 112. The colour filter film 116 is disposed on the protective layer 114 and the first alignment film 118 is disposed on the colour filter film 116.
The second substrate 120 comprises a glass substrate 120a, a transparent electrode layer 122 and a second alignment film 124, wherein the transparent electrode layer 122 comprises Indium-Tin-Oxide (ITO) material. The transparent electrode layer 122 is disposed on the glass substrate 120a and the second alignment film 124 is disposed on the transparent electrode layer 122.
When the reflective LCD displays images, images with different gray scales can be obtained by a range of rotation angles of a plurality of liquid crystal molecules in the liquid crystal layer 130. The rotation angles are determined by an electrical potential difference between the electrode layer 112 and the transparent electrode layer 122 after an external power source is applied thereto.
It is noticeable that the electrical potential difference between the electrode layer 112 and the transparent electrode layer 122 is reduced because their interposed layers share their electrical potential difference and the interposed layers comprise the protective layer 114, the colour filter film 116, the first alignment film 118, the second alignment film 124 and the liquid crystal layer 130. Since the protective layer 114, the colour filter film 116, the first alignment film 118, the second alignment film 124 share the electrical potential difference between the electrode layer 112 and the transparent electrode layer 122, an acquired voltage of the liquid crystal layer 130 is reduced. Thus, these liquid crystal molecules in the liquid crystal layer 130 can not obtain a sufficient voltage in order to be fully rotated and thereby cause the reflective LCD panel 100 to display images with a poor contrast.
Evidently, under a condition of biasing the electrode layer 112 and the transparent electrode layer 122 with a fixed electrical potential difference, thickness reductions of the protective layer 114, the colour filter film 116, the first alignment film 118 and the second alignment film 124 can lower their shared electrical potential difference. Therefore, the acquired voltage of the liquid crystal layer 130 is raised. However, the reflective LCD has a poor colour-displaying performance because of the thickness reduction of the colour filter film 116.
In addition, under a condition of biasing the electrode layer 112 and the transparent electrode layer 122 with a fixed electrical potential difference, since a red colour filter film, a green colour filter film and a blue colour filter film (all not shown), three of which compose the colour filter film 116, have their different reflectance, the reflective LCD panel 100 displays images with a higher dispersion.